Over the course of the exchange, the participants discussed barriers to mitigation strategies and challenges associated with reducing transportation-related emissions due to limits on the types of strategies that MPOs have the power to implement and due to through trips or heavy freight traffic in several areas. Regions also identified some of the synergies between strategies and analysis methods used for criteria pollutants and those used for GHG analysis, while acknowledging some of the key differences between these pollutants.
While land use changes, TDM, traffic flow improvements, transit, and vehicle technology all have the ability to reduce emissions, these strategies do not have the potential to reduce emissions in equivalent amounts. Several MPOs, including SANDAG and SCAG reported that even under scenarios with ambitious land use changes or transit upgrades, these strategies have a limited impact on emissions relative to improvements in fuel economy. Some stakeholders in these and other regions expect greater reductions from these strategies than may be feasible, and so communicating both the importance of pursuing multiple strategies, their synergies where applicable, and their limitations is important.
Modeling and inventory methodologies for GHG inventories, forecasts, and strategy analysis are evolving. For instance, EPA has developed its emissions models over time, most recently switching from MOBILE6.2 to the MOVES model. However, changes in methodology can impact the picture of how much a region emits, where those emissions come from, and any progress it has made toward emissions reduction. Participants from CMAP and SCAG particularly noted the changes from one year to the next using slightly different inventory methods. The changes resulting from new methodologies can also affect the MPO's credibility with stakeholders and the public, who may perceive the previous analysis as an error. Therefore, it is important to communicate what has changed and why.
A number of MPOs present at the exchange, such as NCTCOG, H-GAC, and CHCRPA represent regions where climate change mitigation is controversial. Since these areas are not in conformity under the Clean Air Act, however, they still must implement strategies targeting criteria pollutants such as ozone, NOx, and PM. These include TDM programs, providing infrastructure for transportation alternatives, and programs encouraging the use of cleaner-burning fuels or support of electric-vehicle infrastructure planning.
Peer exchange participants represented diverse constituencies and reported success with a wide range of messages. For example, a number of regions focus only on air quality and public health issues associated with breathing in polluted air. Others, such as California MPOs and Central Lane MPO communicate directly about climate change; while BMC focuses on improving the health of the Chesapeake Bay. One lesson is to tailor messages to an issue that is important to the region's stakeholders. Additionally, since MPOs often are not widely-recognized or understood by the general public, branding specific programs, initiatives, or concepts instead may be more successful.